Method for manufacturing 1,4-bis (4-phenoxybenzoyl)benzene in supersaturation conditions

ABSTRACT

A method for manufacturing 1,4-bis(4-phenoxybenzoylbenzene), including: providing a reactant mixture including terephthaloyl chloride, diphenyl ether and a Lewis acid in a solvent; reacting terephthaloyl chloride with diphenyl ether, so as to obtain a product mixture including a 1,4-bis(4-phenoxybenzoylbenzene)-Lewis acid complex; wherein the 1,4-bis(4-phenoxybenzoylbenzene)-Lewis acid complex is dissolved in the solvent at a 1,4-bis(4-phenoxybenzoylbenzene) weight concentration in the solvent which is higher than the saturation limit of the 1,4-bis(4-phenoxybenzoylbenzene)-Lewis acid complex during at least part of the step of reacting terephthaloyl chloride with diphenyl ether.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of European Application No. 17305561, filed on May 16, 2017. The entire contents of European Application No. 17305559, European Application No. 17305561, European Application No. 17305562, European Application No. 17305581, European Application No. 17305582, and European Application No. 17305583 are hereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present application relates to a method for manufacturing 1,4-bis(4-phenoxybenzoyl)benzene, as well as polyether ketone ketone polymers starting from said 1,4-bis(4-phenoxybenzoyl)benzene.

TECHNICAL BACKGROUND

Polyether ketone ketone (PEKK) polymers have a number of properties which make them useful in applications involving exposure to high temperature or to high mechanical or chemical stress. They are, for instance, useful in the aerospace industry, in off-shore drilling and in medical devices.

One known route for manufacturing polyether ketone ketone polymers relies on the use of 1,4-bis(4-phenoxybenzoyl)benzene as a starting material.

1,4-bis(4-phenoxybenzoyl)benzene can be prepared by reacting terephthaloyl chloride and diphenyl ether in the presence of a Lewis acid such as aluminum trichloride.

In document U.S. Pat. No. 4,816,556 (example 2), 1,4-bis(4-phenoxybenzoyl)benzene is prepared by dissolving terephthaloyl chloride and diphenyl ether in ortho-dichlorobenzene, cooling to 0-5° C. and adding aluminum chloride with temperature kept below 5° C. The mixture is then warmed to 20° C. Thereafter, cold methanol is added so as to produce a slurry which is filtered, reslurried in methanol and filtered again.

In document U.S. Pat. No. 4,826,947 (example 2), 1,4-bis(4-phenoxybenzoyl)benzene is prepared by providing a mixture of methylene chloride, methylsulfone and aluminum trichloride, cooling to a temperature of between −30 and −35° C., and then adding diphenyl ether and thereafter terephthaloyl chloride. The reaction mixture is then poured into cold methanol so as to make a slurry which is then filtered.

Document WO 95/23821 (example 11) discloses providing aluminum chloride in ortho-dichlorobenzene cooled in an ice bath, and then adding terephthaloyl chloride and diphenyl ether. Thereafter, the reaction mixture is allowed to warm up to room temperature, stirred, and poured into a methanol concentrated HCl solution. A precipitate is formed which is subsequently filtered off.

There is still a need for a method for manufacturing 1,4-bis(4-phenoxybenzoyl)benzene with a high purity and a high yield, which can be implemented at the industrial scale in an economically realistic manner.

SUMMARY

It is an object of embodiments of the invention to provide a method for manufacturing 1,4-bis(4-phenoxybenzoyl)benzene, comprising:

-   -   providing a reactant mixture comprising terephthaloyl chloride,         diphenyl ether and a Lewis acid in a solvent;     -   reacting the terephthaloyl chloride with the diphenyl ether, so         as to obtain a product mixture comprising a         1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex;

wherein the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight concentration in the solvent which is higher than the saturation limit of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex during at least part of the step of reacting terephthaloyl chloride with diphenyl ether.

By way of convention, in the present application the concentration of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is indicated by the weight concentration of 1,4-bis(4-phenoxybenzoyl)benzene in the solvent. The same applies to the saturation limit.

In some embodiments, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight concentration which is higher by at least 5%, preferably by at least 10%, more preferably by at least 20%, than the saturation limit of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex, during part of the step of reacting terephthaloyl chloride with diphenyl ether. For example, if the saturation limit is at 20 wt %, then a supersaturation weight concentration of 5% higher would be 5% of the 20 wt %, for a value of 21 wt % (20*1.05).

In some embodiments, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight concentration of more than 5 wt. %, preferably more than 10 wt. %, more preferably more than 15 wt. %, and most preferably more than 30 wt. %, during part of the step of reacting terephthaloyl chloride with diphenyl ether.

In some embodiments, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent during at least 75%, preferably at least 90%, more preferably at least 95% of the duration of the step of reacting terephthaloyl chloride with diphenyl ether, and most preferably during the totality of the step of reacting terephthaloyl chloride with diphenyl ether.

In some embodiments, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 75 mol. %, relative to the initial amount of terephthaloyl chloride, is present in the reactant mixture; preferably the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 80 mol. %, relative to the initial amount of terephthaloyl chloride, is present in the reactant mixture; more preferably the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 85 mol. %, relative to the initial amount of terephthaloyl chloride, is present in the reactant mixture; and most preferably, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 90 mol. %, relative to the initial amount of terephthaloyl chloride, is present in the reactant mixture.

In some embodiments, the step of reacting terephthaloyl chloride with diphenyl ether is performed in a reactor, and:

-   -   the reactor comprises internal walls having a rugosity of less         than 1 μm preferably less than 0.2 μm; and/or     -   the method comprises a preliminary step of washing the reactor;         and/or     -   the method comprises a step of eliminating solid particles from         the reactant mixture, before or after the step of reacting         terephthaloyl chloride with diphenyl ether; and/or     -   the average shear stress for the whole reactant mixture remains         below 100 s⁻¹, preferably below 50 s⁻¹, more preferably below 25         s⁻¹, even more preferably below 20 s⁻¹ during at least part of         the step of reacting terephthaloyl chloride with diphenyl ether.

In some embodiments, the Lewis acid is aluminum trichloride.

In some embodiments, the temperature of the reactant mixture is at least 5° C., preferably at least 15° C. or at least 25° C. or at least 35° C. or at least 45° C. during at least part of the step of reacting terephthaloyl chloride with diphenyl ether.

In some embodiments, the Lewis acid is progressively added to a mixture of terephthaloyl chloride and diphenyl ether in the solvent, and the temperature of the reactant mixture is at least 30° C., preferably at least 40° C. and more preferably at least 45° C., after 30% by weight of Lewis acid has been added, relative to the total weight of Lewis acid.

In some embodiments, the temperature of the reactant mixture increases during the step of reacting terephthaloyl chloride with diphenyl ether, from an initial temperature to a final temperature, and preferably:

-   -   the initial temperature is from 0° C. to 80° C., more preferably         from 30° C. to 50° C., and/or     -   the final temperature is at least 30° C., more preferably at         least 40° C., even more preferably at least 45° C. and most         preferably at least 50° C.

In some embodiments, the solvent is a separate solvent and may be ortho-dichlorobenzene. In some embodiments, the solvent may be diphenyl ether.

In some embodiments, the method comprises the additional steps of:

-   -   mixing the product mixture with a protic solvent so as to         provide a product slurry;     -   separating 1,4-bis(4-phenoxybenzoyl)benzene from the product         slurry, preferably by filtration and optionally washing.

Embodiments of the invention also relate to a method of making a polyether ketone ketone polymer, comprising:

-   -   manufacturing 1,4-bis(4-phenoxybenzoyl)benzene according to the         method described above;     -   reacting said 1,4-bis(4-phenoxybenzoyl)benzene with at least one         difunctional aromatic acyl chloride.

Embodiments of the present invention provide a method for manufacturing 1,4-bis(4-phenoxybenzoyl)benzene with a high purity and a high yield. This method can be implemented at the industrial scale.

In particular, by maintaining the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex which is produced as a supersaturated solution during at least part of the reaction, it was surprisingly discovered that the yield of 1,4-bis(4-phenoxybenzoyl)benzene is increased, and that the level of by-product impurities such as 4-(4-phenoxybenzoyl)benzoyl chloride and its corresponding carboxylic acid and ester forms remains low. Therefore, the method may be more efficient than in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the saturation limit of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex in ortho-dichlorobenzene, as a function of temperature. Temperature in ° C. is provided on the X axis. The weight concentration of 1,4-bis(4-phenoxybenzoyl)benzene at saturation is provided in the Y axis. The Lewis acid-to-1,4-bis(4-phenoxybenzoyl)benzene molar ratio is 4.05. The Lewis acid is aluminum trichloride.

FIG. 2 schematically shows the evolution of the concentration of terephthaloyl chloride (A), 4-(4-phenoxybenzoyl)benzoyl chloride (as defined below) (B), 1,4-bis(4-phenoxybenzoyl)benzene (C) and xanthydrol moiety-containing molecules (D) as a function of the progression of the reaction. The concentrations are provided in mol. % relative to the initial total amount of terephthaloyl chloride. The progression of the reaction is indicated in arbitrary units on the X-axis.

FIG. 3 shows the sum of final amounts of 4-(4-phenoxybenzoyl)benzoyl chloride/4-(4-phenoxybenzoyl)benzoic acid/4-(4-phenoxybenzoyl)benzoic acid ester in the product mixture, in mol. % relative to the initial total amount of terephthaloyl chloride, in 15 different reaction trials.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will now be described in more detail without limitation in the following description.

1,4-bis(4-phenoxybenzoyl)benzene is the compound of formula I:

It may be made by reacting terephthaloyl chloride of formula II:

with diphenyl ether of formula III:

in a solvent, and in the presence of a Lewis acid, acting as a Friedel-Crafts catalyst. This is hereafter called “the reaction step”.

The reaction results in the production of the compound of formula I which is predominantly in the form of a complex with the Lewis acid.

It is believed that the reaction comprises two stages. In the first stage, one molecule of formula II reacts with one molecule of formula III to form the following intermediate of formula IV (4-(4-phenoxybenzoyl)benzoyl chloride) which is called an “active intermediate”:

Then one molecule of the active intermediate of formula IV reacts with another molecule of formula III to form the desired product of formula I.

During the reaction, the following 4-(4-phenoxybenzoyl)benzoic acid of formula IVa can also be produced to some extent (notably from the active intermediate of formula IV):

The corresponding 4-(4-phenoxybenzoyl)benzoic acid ester can be formed either directly from the acyl chloride of formula IV or from the carboxylic acid of formula IVa. The acid form and/or the ester form of the intermediate can be formed during the reaction but they can also primarily be formed from the remaining active intermediate during subsequent workup (such as when the product mixture is mixed with a protic solvent, as described below).

The 4-(4-phenoxybenzoyl)benzoic acid and 4-(4-phenoxybenzoyl)benzoic acid ester are inactive and therefore remain as impurities in the product mixture.

The other main impurities produced by the reaction are xanthydrol moiety-containing molecules.

The solvent may be a non-protic solvent, which can in particular be selected from methylene chloride, carbon disulfide, ortho-dichlorobenzene, meta-dichlorobenzene, para-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,3-trichlorobenzene, ortho-difluorobenzene, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, tetrachloroethylene, dichloromethane, nitrobenzene and mixtures thereof.

Ortho-dichlorobenzene is a preferred solvent.

Lewis acids which may be used include, for example, aluminum trichloride, aluminum tribromide, antimony pentachloride, antimony pentafluoride, indium trichloride, gallium trichloride, boron trichloride, boron trifluoride, zinc chloride, ferric chloride, stannic chloride, titanium tetrachloride, and molybdenum pentachloride. Aluminum trichloride, boron trichloride, aluminum tribromide, titanium tetrachloride, antimony pentachloride, ferric chloride, gallium trichloride, and molybdenum pentachloride are preferred. Aluminum trichloride is preferred.

The reaction between the compounds of formulas II and III to make the compound of formula I may be performed in a reactor. The reactor can be for instance a glass reactor, a glass-lined reactor or a stainless-steel reactor.

According to some variations, the materials introduced into the reactor in the method of embodiments of the invention consist essentially, or consist, of the compounds of formulas II and III, the solvent and the Lewis acid.

According to other variations, the materials introduced into the reactor in the method of embodiments of the invention additionally comprise one or more additives for increasing the solubility of Lewis acid complexes. These additives may notably be selected from Lewis bases such as diphenylsulfone, carboxylic acids, ethers and inorganic salts such as LiCl, NaCl, KCl, CaCl₂ and MgCl₂, as well as mixtures thereof.

According to embodiments of the invention, an initial reactant mixture comprising (and preferably consisting of) terephthaloyl chloride and diphenyl ether in a solvent is provided. The reactant mixture can be made by mixing the three components together, in any order. By way of example, the solvent can be introduced first into the reactor, and then the two reactants can be added to the reactor.

As a second step, the Lewis acid is added to the reactant mixture. Preferably, the Lewis acid is added as a solid. Alternatively, it can also be added as a suspension or a solution, preferably in the abovementioned solvent.

In some variations, the Lewis acid is added in a particulate form, such as in the form of granules (having, e.g., a Dv80 of more than 1 mm) or in the form of a powder (having, e.g., a Dv80 of less than 1 mm, and preferably a Dv50 of less than 0.5 mm). Dv80 and Dv50 are respectively the particle sizes at the 80^(th) and 50^(th) percentiles (in volume) of the cumulative size distribution of the Lewis acid particles. These parameters may be determined by sieving.

In some particular embodiments, the weight concentrations and weight ratios of the reactants and of the catalyst are as follows:

-   -   the concentration of terephthaloyl chloride (relative to the sum         of solvent, terephthaloyl chloride, diphenyl ether and Lewis         acid introduced into the reactor) is from 3 to 12%, preferably         from 5 to 10%;     -   the concentration of diphenyl ether (relative to the sum of         solvent, terephthaloyl chloride, diphenyl ether and Lewis acid         introduced into the reactor) is from 5 to 35%, preferably from         12 to 25%;     -   the concentration of Lewis acid (relative to the sum of solvent,         terephthaloyl chloride, diphenyl ether and Lewis acid introduced         into the reactor) is from 4 to 30%, preferably from 10 to 25%;     -   the weight ratio of terephthaloyl chloride to diphenyl ether         introduced into the reactor is from 0.2 to 0.6, preferably from         0.3 to 0.5;     -   the weight ratio of Lewis acid to terephthaloyl chloride plus         diphenyl ether introduced into the reactor is from 0.2 to 0.9,         preferably from 0.3 to 0.7.

The addition of the Lewis acid is preferably performed progressively, over a period of time which can advantageously range from 5 to 600 minutes, preferably from 30 to 300 minutes.

The addition can be performed continuously or with one or more interruptions. If it is performed continuously, it can be conducted at a constant rate of addition. Alternatively, the rate of addition can vary over time.

The reactant mixture may be agitated during at least part of the reaction step. Thus, the reactor is preferably provided with an agitation device such as a mechanical stirrer (which may, e.g., comprise one or more impellers) or a recirculation loop with a pump.

Preferably, the reactant mixture may be agitated using the agitation device during the addition of the Lewis acid.

Once the addition of the Lewis acid to the reactant mixture is complete, the reaction step may optionally comprise a step of maintaining the reactant mixture, preferably under agitation, for a certain time, in order to complete the reaction to the desired degree. Preferably, the mixture is maintained from 0 to 600 min, more preferably from 5 to 180 min.

Once the reaction is completed to the desired degree, the reactant mixture becomes designated as a product mixture.

The end of the reaction step corresponds to the beginning of the next step in the method, which is usually a purification step, as described in more detail below.

During the reaction step, 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is initially produced as a dissolved species, the concentration of which progressively increases. According to embodiments of the present invention, at some point of time during the reaction step, the concentration of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex exceeds the saturation limit of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex. In other terms, according to embodiments of the invention, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is maintained in a supersaturated state during at least part of the step of reacting terephthaloyl chloride with diphenyl ether.

This saturation limit depends on the conditions of the reactant mixture in real time and may vary during the reaction step. In particular, it depends on the temperature of the reactant mixture, the nature of the solvent and the amount of Lewis-acid.

The 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is said to be in a supersaturated state when it is dissolved in the reactant mixture at a concentration exceeding the saturation limit. The supersaturated state is a metastable state. Therefore, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex in a supersaturated state is able to suddenly precipitate if a nucleating agent (e.g., solid particles) is present in the reactant mixture.

By way of convention, in the present application the concentration of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is indicated by the weight concentration of 1,4-bis(4-phenoxybenzoyl)benzene in the solvent. The same applies to the saturation limit.

The saturation limit can be determined using the following model experiment: predetermined quantities of 1,4-bis(4-phenoxybenzoyl)benzene and Lewis acid are added to a given solvent contained in a glass tube. The contents of the glass tube are agitated by magnetic stirring. The temperature of the mixture within the tube is controlled by placing the tube in a thermofluid. The initial temperature is such that the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is initially present as a suspension in the solvent. Then the temperature is gradually increased until the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex gets fully solubilized in the solvent. At this particular temperature, the saturation limit is equal to the weight concentration of 1,4-bis(4-phenoxybenzoyl)benzene in the mixture. The experiment can be repeated a number of times using another weight concentration of 1,4-bis(4-phenoxybenzoyl)benzene and the same weight ratio of Lewis acid with respect to 1,4-bis(4-phenoxybenzoyl)benzene, so that a temperature/saturation curve can be finally obtained for a given solvent and a given weight ratio of Lewis acid to 1,4-bis(4-phenoxybenzoyl)benzene.

FIG. 1 shows by way of illustration the temperature/saturation curve obtained as described above in ortho-dichlorobenzene as a solvent, with a Lewis acid-to-1,4-bis(4-phenoxybenzoyl)benzene molar ratio of 4.05. If the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent at a certain temperature and at a certain weight concentration of 1,4-bis(4-phenoxybenzoyl)benzene and if the corresponding temperature/concentration point is situated above the curve, then the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is in the supersaturated state.

It has been found by the present inventors that maintaining the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex in a supersaturated state during part of the reaction step can result in an increased yield.

The phenomenon at stake is schematically illustrated in FIG. 2, which shows the typical evolution of the concentration of the relevant species in the reactant mixture during the reaction step. It can be seen that, as terephthaloyl chloride (A) is consumed, the 4-(4-phenoxybenzoyl)benzoyl chloride (B) is initially produced in a large amount. Then the concentration of 4-(4-phenoxybenzoyl)benzoyl chloride in the reactant mixture reaches a peak and decreases, while the concentration of the desired product (C) increases. The amount of xanthydrol moiety-containing impurities (D) increases over time but remains at a relatively low level.

If the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex precipitates during the reaction step, it is believed (without wishing to be bound by any theory) that part of the unreacted 4-(4-phenoxybenzoyl)benzoyl chloride is caught in the precipitate and thus substantially prevented from further reacting. In other terms, after the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex has precipitated, it is believed that the conversion of the remaining 4-(4-phenoxybenzoyl)benzoyl chloride (B) to the desired product (C) is significantly impeded.

Therefore, in accordance with embodiments the present invention, this precipitation is either prevented or at least postponed during the reaction step, without however keeping the concentration of 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex in the mixture at a low level, which would in turn reduce the overall efficiency and kinetics of the reaction. This is made possible because the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex remains dissolved in the solvent during at least part of the reaction step even after its concentration has reached the saturation limit.

According to some variations, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex precipitates at some point of time during the reaction step (after the concentration of this species has exceeded the saturation limit).

According to alternative variations, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex does not precipitate during the reaction step and remains dissolved in the solvent during the entirety of the reaction step. In certain embodiments, as soon as some solid precipitate is generated, it may act as a seed and precipitate all, or at least most, of the EKKE above saturation limit. In certain embodiments, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex may be considered to be without precipitation when at least 96%, or at least 98% or at least 99% or at least 99.5% by weight of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex in excess to the saturation limit has not precipitated.

Preferably, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent during at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, or at least 99% of the overall duration of the reaction step.

Preferably, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is still dissolved in the solvent (i.e., has not precipitated), when it is present in an amount of 75 mol. %, (or in other variations 80 mol. %, or 85 mol. %, or 90 mol. %, or 91 mol. %, or 92 mol. %, or 93 mol. %, or 94 mol. %, or 95 mol. %) in the reactant mixture, said amount being expressed as the amount of 1,4-bis(4-phenoxybenzoyl)benzene relative to the initial amount of terephthaloyl chloride reactant which was introduced.

Preferably, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight concentration which is higher by at least 5%, (or in other variations by at least 10%, or 15%, or 20%, or 25%, or 30%, or 35%, or 40%) than the saturation limit of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex, during part of the reaction step, and for instance during at least 5 minutes, or at least 10 minutes, or at least 15 minutes, or at least 20 minutes, or at least 30 minutes, or at least 40 minutes, or at least 1 hour.

Preferably, the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent (without precipitation) at a 1,4-bis(4-phenoxybenzoyl)benzene concentration of more than 5 wt. %, or more than 10 wt. %, or more than 15 wt. %, or more than 20 wt. %, or more than 25 wt. %, or more than 30 wt. %, or more than 35 wt. %, or more than 40 wt. %, or more than 50 wt. %, during part of the reaction step.

In order to carry out the embodiments of invention and to maintain the concentration of dissolved 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex in the solvent above the saturation limit, nucleation of the precipitate should be prevented or at least delayed. Several measures can be taken in this respect, in a non-limiting manner.

First, the internal walls of the reactor (which are in contact with the reactant mixture) should have a low surface roughness. Preferably, the surface roughness Ra (as defined in ISO 4287) of the walls may be less than 2 μm, or less than 1 μm, or less than 0.8 μm, or less than 0.5 μm, or less than 0.2 μm.

Similarly, all equipment surfaces in contact with the reactant mixture during the reaction step, such as the surfaces of an impeller (if any) or the internal surfaces of a recirculation loop, may also have a rugosity of less than 2 μm, or less than 1 μm, or less than 0.8 μm, or less than 0.5 μm, or less than 0.2 μm.

Second, the method may comprise a preliminary step of washing the reactor, in order to eliminate all solid residues, such as dust particles or residual product particles from a previous reaction, before providing the reactant mixture in the reactor. As an example, this can be achieved by spraying or blasting a liquid or a solid or a suspension on reactor wall, preferably the reaction solvent, or by filling the reactor with a liquid or a suspension under agitation, or by any mechanical action.

For example, the step of washing the reactor may be frequent, at least once every 10 batch, preferably every 5 batch, even more preferably every batch.

Third, the method may comprise a step of eliminating solid particles from the reactant mixture, either before the start of the reaction step or during the reaction step, such as by filtration (including, e.g., ultrafiltration).

Fourth, the conditions (in particular intensity) of agitation during the reaction step may be selected in such a manner that the average shear stress (calculated as the product K_(mo)×N where K_(mo) is the Metzner-Otto constant for the impellers used and N is the rotation frequency) for the reactant mixture remains below 100 s⁻¹, preferably below 50 s⁻¹, more preferably below 25 s⁻¹, even more preferably below 20 s⁻¹ during at least part of the reaction step, and more particularly during the part of the reaction step when the concentration of the dissolved 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex in the solvent is above the saturation limit (such as during the last 5%, or the last 10%, or the last 15%, or the last 20%, or the last 25%, or the last 30%, or the last 35%, or the last 40%, or the last 45%, or the last 50% of the reaction step, relative to the overall duration of the reaction step).

The reaction at stake is exothermic. Preferably, a temperature control system is provided, in order to control the temperature of the reactant mixture in the reactor, in particular during and after addition of the Lewis acid. The temperature control system may in particular comprise a temperature sensor within the reactor and may be configured to cool and/or to heat the reactant mixture. Preferably, it is at least configured to cool the reactant mixture.

Devices for heating and/or cooling the reactant mixture may include a heat exchanger inside the reactor or in a recirculation loop, or a heat exchange fluid circuit in the jacket of the reactor.

When the temperature of the reactant mixture increases during the step of adding the Lewis acid, this can be achieved in three different manners:

-   -   by heating the reactant mixture (while preferably also         controlling the rate of addition of the Lewis acid, so as to         achieve a targeted increase in temperature);     -   by simply controlling the rate of addition of the Lewis acid so         as to achieve a targeted increase in temperature, without         providing external cooling or heating; or     -   by cooling the reactant mixture, while also controlling the rate         of addition of the Lewis acid, so as to achieve a targeted         increase in temperature

According to a preferred embodiment, the reactant mixture is cooled during and possibly also after the step of adding the Lewis acid, in order to prevent an excessively large or rapid increase in temperature of the reactant mixture as the reactants start reacting with each other.

Preferably, the temperature of the reactant mixture is greater than 5° C. during at least part of the step of adding the Lewis acid to the reactant mixture. In particular variations, the temperature of the reactant mixture is at least 10° C., or at least 15° C., or at least 20° C., or at least 25° C., or at least 30° C., or at least 35° C., or at least 40° C., or at least 45° C., or at least 50° C., or at least 55° C., or at least 60° C., during at least part of the step of adding the Lewis acid to the reactant mixture.

It should be noted that, when the temperature is higher, the saturation limit of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is also higher, so that a relatively high temperature during at least part of the reaction step is useful for preventing or delaying the undesired precipitation of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex. Accordingly, embodiments of the present invention require a concentration higher than the current saturation limit (e.g., at the present conditions (e.g., temperature and pressure).

Besides, it has surprisingly been found that conducting the reaction step at a relatively high temperature, results in an increase in the yield of 1,4-bis(4-phenoxybenzoyl)benzene, without any significant increase in the level of by-product impurities such as xanthydrol moiety-containing molecules.

On the other hand, the temperature during the step of adding the Lewis acid to the reactant mixture should preferably remain below a certain threshold, for example, 120° C., in order to avoid any significant polymerization of the reactants into a PEKK polymer.

Furthermore, the temperature during the step of adding the Lewis acid to the reactant mixture should remain below the boiling temperature of the solvent.

It is possible to operate the reactor in a pressurized manner so that the temperature in the reactor can reach a higher value without causing the solvent to boil. In this case, the pressure in the reactor can range from 1 bar (atmospheric pressure) to 6 bar, preferably from 1.5 bar to 3 bar.

Alternatively, and preferably, the reaction is performed at atmospheric pressure.

According to some variants, the temperature of the reactant mixture does not exceed 100° C., preferably 90° C., more preferably 80° C., even more preferably 70° C., during the step of adding the Lewis acid.

It is believed that it may be more beneficial for the temperature of the reactant mixture to be relatively high at the end of the step of adding the Lewis acid than at the beginning of this step, in order to achieve some or all of the advantageous effects of embodiments of the invention.

Accordingly, in some variants, once 90% by weight of Lewis acid has been added to the reactant mixture (relative to the total weight of Lewis acid added to the reactant mixture), it is preferred that the temperature of the reactant mixture is and remains of at least 5° C., preferably at least 10° C., or at least 15° C., or at least 20° C., or at least 25° C., or at least 30° C., or at least 35° C., or at least 40° C., or at least 45° C., or at least 50° C., or at least 55° C., or at least 60° C., during the remainder of the step of adding the Lewis acid to the reactant mixture.

In some variants, once 75% by weight of Lewis acid has been added to the reactant mixture (relative to the total weight of Lewis acid added to the reactant mixture), it is preferred that the temperature of the reactant mixture is and remains of at least 5° C., preferably at least 10° C., or at least 15° C., or at least 20° C., or at least 25° C., or at least 30° C., or at least 35° C., or at least 40° C., or at least 45° C., or at least 50° C., or at least 55° C., or at least 60° C., during the remainder of the step of adding the Lewis acid to the reactant mixture.

In some variants, once 50% by weight of Lewis acid has been added to the reactant mixture (relative to the total weight of Lewis acid added to the reactant mixture), it is preferred that the temperature of the reactant mixture is and remains of at least 5° C., preferably at least 10° C., or at least 15° C., or at least 20° C., or at least 25° C., or at least 30° C., or at least 35° C., or at least 40° C., or at least 45° C., or at least 50° C., or at least 55° C., or at least 60° C., during the remainder of the step of adding the Lewis acid to the reactant mixture.

In some variants, once 20% by weight of Lewis acid has been added to the reactant mixture (relative to the total weight of Lewis acid added to the reactant mixture), it is preferred that the temperature of the reactant mixture is and remains of at least 5° C., preferably at least 10° C., or at least 15° C., or at least 20° C., or at least 25° C., or at least 30° C., or at least 35° C., or at least 40° C., or at least 45° C., or at least 50° C., or at least 55° C., or at least 60° C., during the remainder of the step of adding the Lewis acid to the reactant mixture.

The temperature of the reactant mixture can remain constant during the step of adding the Lewis acid. Alternatively, it can vary during this step.

By “initial temperature” is meant the temperature of the reactant mixture at the beginning of the step of adding the Lewis acid, i.e., as the first molecules of Lewis acid are added to the reactant mixture.

By “final temperature” is meant the temperature of the reactant mixture at the end of the step of adding the Lewis acid, i.e., as the last molecules of Lewis acid are added to the reactant mixture.

The initial temperature of the reactant mixture may range from, e.g., −30° C. to 80° C. In some variations, the initial temperature of the reactant mixture is from −30 to −25° C.; or from −25 to −20° C.; or from −20 to −15° C.; or from −15 to −10° C.; or from −10 to −5° C.; or from −5 to −0° C.; or from 0 to 5° C.; or from 5 to 10° C.; or from 10 to 15° C.; or from 15 to 20° C.; or from 20 to 25° C.; or from 25 to 30° C.; or from 30 to 35° C.; or from 35 to 40° C.; or from 40 to 45° C.; or from 45 to 50° C.; or from 50 to 55° C.; or from 55 to 60° C.; or from 60 to 65° C.; or from 65 to 70° C.; or from 70 to 75° C.; or from 75 to 80° C. Ranges of from 0 to 80° C., more particularly from 20 to 50° C. are preferred.

The final temperature of the reactant mixture may range from, e.g., 10° C. to 80° C. In some variations, the final temperature of the reactant mixture is from 10 to 15° C.; or from 15 to 20° C.; or from 20 to 25° C.; or from 25 to 30° C.; or from 30 to 35° C.; or from 35 to 40° C.; or from 40 to 45° C.; or from 45 to 50° C.; or from 50 to 55° C.; or from 55 to 60° C.; or from 60 to 65° C.; or from 65 to 70° C.; or from 70 to 75° C.; or from 75 to 80° C. Ranges of from 30 to 80° C., and more particularly from 40 to 70° C., even more particularly from 45 to 60° C. are preferred. In some variations, the final temperature is at least 30° C., preferably at least 40° C., more preferably at least 45° C. and most preferably at least 50° C.

In some variations, the temperature of the reactant mixture decreases during the step of adding the Lewis acid, i.e., the final temperature is lower than the initial temperature.

In preferred variations, the temperature of the reactant mixture increases during the step of adding the Lewis acid, i.e., the final temperature is greater than the initial temperature.

In some embodiments, the temperature difference ΔT between the final temperature and the initial temperature is from 5 to 60° C., preferably from 10 to 50° C., more preferably from 20 to 40° C.

In some variations, the increase in temperature is monotonous, i.e., there is no transient decrease in temperature during the entire step of adding the Lewis acid. On the other hand, transient variations or fluctuations in temperature are possible in some embodiments, especially due to the non-instantaneous nature of the temperature control.

In some variations, the temperature of the reactant mixture continuously increases from the initial temperature to the final temperature. Alternatively, the temperature of the reactant mixture may comprise one or more increase stages and one more plateau stages during the step of adding the Lewis acid. In particular, the temperature of the reactant mixture may initially increase during a first part of the step of adding the Lewis acid, from the initial temperature to the final temperature, and then plateau at the final temperature during a second part of the step of adding the Lewis acid. In this case, the plateau temperature may be set with a precision of, e.g., +/−5° C., or +/−2° C., or +/−1° C.

There is no limitation as to the temperature of the reactant mixture during the optional step of maintaining the reactant mixture, after the addition of the Lewis acid. In some variations, the temperature of the mixture is maintained at the final temperature described above. In other variations, it increases or decreases relative to the final temperature.

The method of embodiments of the invention advantageously comprises one or more steps (after the reaction step) for purifying 1,4-bis(4-phenoxybenzoyl)benzene from the product mixture, and in particular from the solvent, catalyst and unreacted reactants as well as by-products. The purification may comprise the steps of:

-   -   mixing the product mixture with a protic solvent so as to         provide a product slurry;     -   separating 1,4-bis(4-phenoxybenzoyl)benzene from the product         slurry, preferably by filtration and washing.

The protic solvent used to make the product slurry is advantageously selected so that 1,4-bis(4-phenoxybenzoyl)benzene tends to easily precipitate. By way of example, methanol may be used as a protic solvent.

The protic solvent can be an organic solvent, such as methanol, acetic acid, formic acid, ethanol, isopropanol, and benzyl alcohol.

Alternatively, the protic solvent can be an aqueous solution.

Mixtures of the above solvents can also be used, such as an aqueous-organic solvent, e.g., an aqueous solution mixed with methanol.

The desired product can then be recovered from the product slurry by filtration. If necessary, the product can be washed, preferably by a protic solvent such as methanol, and filtrated again, once or several times. Washing can be performed for example by re-slurrying the product in the solvent.

The 1,4-bis(4-phenoxybenzoyl)benzene obtained according to embodiments of the invention can subsequently be used to perform a polymerization reaction so as to make a PEKK polymer.

In order to make the PEKK polymer, 1,4-bis(4-phenoxybenzoyl)benzene is reacted with at least one difunctional aromatic acyl chloride.

The difunctional aromatic acyl chloride may in particular include terephthaloyl chloride, isophthaloyl chloride and more preferably a mixture of terephthaloyl chloride and isophthaloyl chloride.

The reaction is preferably implemented in a solvent. The solvent is preferably a non-protic solvent, which can in particular be selected from methylene chloride, carbon disulfide, ortho-dichlorobenzene, meta-dichlorobenzene, para-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,3-trichlorobenzene, ortho-difluorobenzene, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, tetrachloroethylene, dichloromethane, nitrobenzene and mixtures thereof.

The reaction is preferably implemented in the presence of a Lewis acid as a catalyst.

Lewis acids which may be used include, for example, aluminum trichloride, aluminum tribromide, antimony pentachloride, antimony pentafluoride, indium trichloride, gallium trichloride, boron trichloride, boron trifluoride, zinc chloride, ferric chloride, stannic chloride, titanium tetrachloride, and molybdenum pentachloride. Aluminum trichloride, boron trichloride, aluminum tribromide, titanium tetrachloride, antimony pentachloride, ferric chloride, gallium trichloride, and molybdenum pentachloride are preferred. Aluminum trichloride is particularly preferred.

The polymerization can be implemented in the same reactor as the one used for the production of 1,4-bis(4-phenoxybenzoyl)benzene. But more preferably it is implemented in one or more other reactors.

The polymerization can be carried out at a temperature ranging from, e.g., 50 to 120° C.

The method of making the PEKK polymer advantageously also comprises one or more steps for purifying the PEKK polymer, such as steps of:

-   -   mixing the mixture containing the PEKK polymer with a protic         solvent so as to provide a PEKK slurry;     -   separating the PEKK polymer from the PEKK slurry, preferably by         filtration and washing.

The protic solvent used to make the PEKK slurry may be, e.g., methanol.

The PEKK polymer can then be recovered from the PEKK slurry by filtration. If necessary, the polymer can be washed, preferably by a protic solvent such as methanol, and filtrated again, once or several times. Washing can be performed for example by re-slurrying the polymer in the solvent.

Example

The following example illustrates embodiments of the invention without limiting the invention.

In a 2 L reactor equipped with a mechanical stirrer, with a nitrogen inlet and outlet going to a scrubber system, 1470 g of ortho-dichlorobenzene, 92.7 g of terephthaloyle chloride and 233 g of diphenyloxide were introduced.

After full solubilization, the temperature of the mixture was set at 25° C. While keeping the temperature at 25° C., 198 g of AlCl₃ were slowly added to the reactant mixture. After completion of AlCl₃ addition, the mixture was kept agitated at 25° C. during 3 hours to finish the reaction. Then a sample was taken, quenched in methanol and analyzed with 1H NMR. The relative molar composition was calculated based on the characteristic peaks of each impurity formed from terephthaloyl chloride.

Fifteen different analogous trials were performed. The molar concentration of 4-(4-phenoxybenzoyl)benzoyl chloride and corresponding carboxylic acid and ester impurities (relative to the initial amount of introduced terephthaloyl chloride) is shown on FIG. 3. In trials 1-9 (comparative trials), precipitation occurred during the reaction step. In trials 10-15 (according to embodiments of the invention), no precipitation, for example, no visible precipitation, occurred during the reaction step even after the concentration of 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex in the solvent exceeded the saturation limit, resulting in a much better overall yield of the synthesis. In all fifteen trials, the molar content of xanthydrol moiety-containing impurities (relative to the initial amount of introduced terephthaloyl chloride) was relatively constant, between 4.3% and 5.1%.

Embodiments

-   1. A method for manufacturing 1,4-bis(4-phenoxybenzoyl)benzene,     comprising:     -   providing a reactant mixture comprising terephthaloyl chloride,         diphenyl ether and a Lewis acid in a solvent;     -   reacting the terephthaloyl chloride with the diphenyl ether, so         as to obtain a product mixture comprising a         1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex;     -   wherein the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex         is dissolved in the solvent at a         1,4-bis(4-phenoxybenzoyl)benzene weight concentration in the         solvent which is higher than the saturation limit of the         1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex during at         least part of the step of reacting terephthaloyl chloride with         diphenyl ether. -   2. The method of embodiment 1, wherein the     1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in     the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight     concentration which is higher by at least 5%, preferably by at least     10%, more preferably by at least 20%, than the saturation limit of     the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex, during part     of the step of reacting terephthaloyl chloride with diphenyl ether. -   3. The method of embodiment 1 or 2, wherein the     1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in     the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight     concentration of more than 5 wt. %, preferably more than 10 wt. %,     more preferably more than 15 wt. %, and most preferably more than 30     wt. %, during part of the step of reacting terephthaloyl chloride     with diphenyl ether. -   4. The method of any one of embodiments 1 to 3, wherein the     1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in     the solvent during at least 75%, preferably at least 90%, more     preferably at least 95% of the duration of the step of reacting     terephthaloyl chloride with diphenyl ether, and most preferably     during the totality of the step of reacting terephthaloyl chloride     with diphenyl ether. -   5. The method of any one of embodiments 1 to 4, wherein the     1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in     the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 75     mol. %, relative to the initial amount of terephthaloyl chloride, is     present in the reactant mixture; preferably the     1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in     the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 80     mol. %, relative to the initial amount of terephthaloyl chloride, is     present in the reactant mixture; more preferably the     1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in     the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 85     mol. %, relative to the initial amount of terephthaloyl chloride, is     present in the reactant mixture; and most preferably, the     1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in     the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 90     mol. %, relative to the initial amount of terephthaloyl chloride, is     present in the reactant mixture. -   6. The method of any one of embodiments 1 to 5, wherein the step of     reacting terephthaloyl chloride with diphenyl ether is performed in     a reactor, and wherein:     -   the reactor comprises internal walls having a rugosity of less         than 1 μm preferably less than 0.2 μm; and/or     -   the method comprises a preliminary step of washing the reactor;         and/or     -   the method comprises a step of eliminating solid particles from         the reactant mixture, before or after the step of reacting         terephthaloyl chloride with diphenyl ether; and/or     -   the shear stress of the reactant mixture remains below 100 s⁻¹,         preferably below 25 s⁻¹ during at least part of the step of         reacting terephthaloyl chloride with diphenyl ether. -   7. The method of any one of embodiments 1 to 6, wherein the Lewis     acid is aluminum trichloride. -   8. The method of any one of embodiments 1 to 7, wherein the     temperature of the reactant mixture is at least 5° C., preferably at     least 15° C. or at least 25° C. or at least 35° C. or at least     45° C. during at least part of the step of reacting terephthaloyl     chloride with diphenyl ether. -   9. The method of any one of embodiments 1 to 8, wherein the Lewis     acid is progressively added to a mixture of terephthaloyl chloride     and diphenyl ether in the solvent, and the temperature of the     reactant mixture is at least 30° C., preferably at least 40° C. and     more preferably at least 45° C., after 30% by weight of Lewis acid     has been added, relative to the total weight of Lewis acid. -   10. The method of any one of embodiments 1 to 9, wherein the     temperature of the reactant mixture increases during the step of     reacting terephthaloyl chloride with diphenyl ether, from an initial     temperature to a final temperature, and wherein, preferably:     -   the initial temperature is from 0° C. to 80° C., more preferably         from 30° C. to 50° C., and/or     -   the final temperature is at least 30° C., more preferably at         least 40° C., even more preferably at least 45° C. and most         preferably at least 50° C. -   11. The method of any one of embodiments 1 to 10, wherein the     solvent is ortho-dichlorobenzene. -   12. The method of any one of embodiments 1 to 11, comprising the     additional steps of:     -   mixing the product mixture with a protic solvent so as to         provide a product slurry;     -   separating 1,4-bis(4-phenoxybenzoyl)benzene from the product         slurry, preferably by filtration and optionally washing. -   13. A method of making a polyether ketone ketone polymer,     comprising:     -   manufacturing 1,4-bis(4-phenoxybenzoyl)benzene according to the         method of any one of embodiments 1 to 12;     -   reacting said 1,4-bis(4-phenoxybenzoyl)benzene with at least one         difunctional aromatic acyl chloride. 

The invention claimed is:
 1. A method for manufacturing 1,4-bis(4-phenoxybenzoyl)benzene, comprising: providing a reactant mixture comprising terephthaloyl chloride, diphenyl ether and a Lewis acid in a solvent; reacting the terephthaloyl chloride with the diphenyl ether, so as to obtain a product mixture comprising a 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex; wherein the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight concentration in the solvent which is higher than the saturation limit of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex during at least part of the step of reacting terephthaloyl chloride with diphenyl ether.
 2. The method of claim 1, wherein the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight concentration which is higher by at least 5% than the saturation limit of the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex, during part of the step of reacting terephthaloyl chloride with diphenyl ether.
 3. The method of claim 1, wherein the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent at a 1,4-bis(4-phenoxybenzoyl)benzene weight concentration of more than 5 wt. % during part of the step of reacting terephthaloyl chloride with diphenyl ether.
 4. The method of claim 1, wherein the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent during at least 75% of the duration of the step of reacting terephthaloyl chloride with diphenyl ether.
 5. The method of claim 1, wherein the 1,4-bis(4-phenoxybenzoyl)benzene-Lewis acid complex is dissolved in the solvent when an amount of 1,4-bis(4-phenoxybenzoyl)benzene of 75 mol. %, relative to the initial amount of terephthaloyl chloride, is present in the reactant mixture.
 6. The method of claim 1, wherein the step of reacting terephthaloyl chloride with diphenyl ether is performed in a reactor, and wherein: the reactor comprises internal walls having a rugosity of less than 1 μm; and/or the method comprises a preliminary step of washing the reactor; and/or the method comprises a step of eliminating solid particles from the reactant mixture, before or after the step of reacting terephthaloyl chloride with diphenyl ether; and/or the shear stress of the reactant mixture remains below 100 s⁻¹ during at least part of the step of reacting terephthaloyl chloride with diphenyl ether.
 7. The method of claim 1, wherein the Lewis acid is aluminum trichloride.
 8. The method of claim 1, wherein the temperature of the reactant mixture is at least 5° C. during at least part of the step of reacting terephthaloyl chloride with diphenyl ether.
 9. The method of claim 1, wherein the Lewis acid is progressively added to a mixture of terephthaloyl chloride and diphenyl ether in the solvent, and the temperature of the reactant mixture is at least 30° C. after 30% by weight of Lewis acid has been added, relative to the total weight of Lewis acid.
 10. The method of claim 1, wherein the temperature of the reactant mixture increases during the step of reacting terephthaloyl chloride with diphenyl ether, from an initial temperature to a final temperature.
 11. The method of claim 1, wherein the solvent is ortho-dichlorobenzene.
 12. The method of claim 1, comprising the additional steps of: mixing the product mixture with a protic solvent so as to provide a product slurry; separating 1,4-bis(4-phenoxybenzoyl)benzene from the product slurry and optionally washing.
 13. A method of making a polyether ketone ketone polymer, comprising: manufacturing 1,4-bis(4-phenoxybenzoyl)benzene according to the method of claim 1; reacting said 1,4-bis(4-phenoxybenzoyl)benzene with at least one difunctional aromatic acyl chloride. 